# Ultrasound attenuation of superfluid $^{3}$He in aerogel

## TL;DR

This study measures ultrasound attenuation in superfluid helium-3 within aerogel, revealing unique behavior at low temperatures consistent with theories of gapless excitations and collision drag effects.

## Contribution

First direct measurement of ultrasound attenuation in superfluid helium-3 in aerogel across a wide pressure range at zero magnetic field.

## Key findings

- Attenuation behavior differs significantly from bulk helium-3.
- Results align with theories involving gapless excitations.
- Evidence supports collision drag effects in superfluid aerogel.

## Abstract

We have performed longitudinal ultrasound (9.5 MHz) attenuation measurements in the B-phase of superfluid $^3$He in 98% porosity aerogel down to the zero temperature limit for a wide range of pressures at zero magnetic field. The absolute attenuation was determined by direct transmission of sound pulses. Compared to the bulk fluid, our results revealed a drastically different behavior in attenuation, which is consistent with theoretical accounts with gapless excitations and a collision drag effect.